The present invention relates to a flow detector suitable for detecting a fluid flow at any position in a piping circuit for controlling the fluid.
In the past, flow detectors of differential transformer type have been proposed as disclosed in the Japanese Patent Unexamined Publication Nos. 61-231416 and 49-75055 and as described in the Japanese Utility Model Application Nos. 62-20553, 62-20554 and 62-20555.
Such conventional flow detectors have the following problems. That is to say, firstly, the flow detector cannot detect a fluid flow when a difference in pressure between a fluid inlet and a fluid outlet thereof is very small and the flowing speed of the fluid passing therethrough is very slow. Secondly, since the flow detector itself is large-sized, it is difficult to incorporate the flow detector into a piping circuit for controlling the fluid. Thirdly, since the level of a signal outputted from the flow detector is too low, it is necessary to provide an amplifier circuit. Lastly, since a large stroke of a piston including a magnetic member is required for obtaining an optimum signal, a body of the flow detector will be over-sized.